Known in the art is stratified combustion using fuel injected in a compression stroke to form a combustible air-fuel mixture in just part of the inside of the cylinder and igniting and burning this combustible air-fuel mixture by a spark plug so as to enable combustion making the air-fuel ratio of the inside of the cylinder as a whole leaner than the stoichiometric air-fuel ratio. At the time of stratified combustion, it is necessary to position the spark gap of the spark plug inside the combustible air-fuel mixture at the ignition timing. For this, it is proposed to bias the injected fuel for forming the combustible air-fuel mixture in the spark plug direction by a cavity formed in the piston top face, but due to this, the fuel injection timing would be limited by the piston position.
To enable the fuel injection timing to be set without such a limitation, there has been proposed a direct fuel injection-type spark-ignition internal combustion engine designed to make the fuel injected from a fuel injector arranged at the approximate center of the top of the cylinder form a combustible air-fuel mixture during its flight inside the cylinder and ignite and burn this combustible air-fuel mixture by a spark plug arranged in the flight path of the injected fuel so as to realize good stratified combustion (for example, see Japanese Patent Publication (A) No. 2005-105877, Japanese Patent Publication (A) No. 9-209762, Japanese Patent Publication (A) No. 11-182247, and Japanese Patent Publication (A) No. 2004-340040).
In the above background art, the fuel injector injects fuel in a hollow conical shape, but even if just injecting fuel in this way, the injected fuel will not form a good combustible air-fuel mixture sufficiently mixed with intake air during its flight before reaching the piston top face or cylinder bore and good stratified combustion can not be realized as designed.
Therefore, an object of the present invention is to provide a direct fuel injection-type spark-ignition internal combustion engine reliably making the fuel injected from the fuel injector a good combustible air-fuel mixture during flight and igniting and burning this combustible air-fuel mixture by a spark plug to enable realization of good stratified combustion.